The invention relates to a method for the separation of a first liquid from a second one, in particular for the separation of water droplets from oil or, conversely, of oil droplets from water.
Oil from mineral sources, namely petroleum or so-called condensate, as a rule contains water as a result of geological processes, of sea water intrusions into oil and/or gas fields, or of injected pressurized water which has been introduced during the extracting of the oil for the maintaining of the pressure in the oil field. Condensate is a liquid consisting of heavy hydrocarbons which arise as accompanying substances in the winning of the natural gas and which are separated from the gas. In the following the terms oil and petroleum shall also comprise the condensate.
Water can be tolerated only in small amounts in oil which is supplied to refineries as a raw material due to corrosion in transport ships or forwarding pipes, due to transport costs for valueless water and due to fractionating processes in the refineries, which can mostly be carried out only in the absence of water. As a rule an oil which is transported by tankers must not contain more than 1% water.
In a known apparatus ("operformax coalescer"), which is formed as a cylindrical and horizontally arranged container, phases of a mixture which consists of the three phases gas, oil and water in the form of very fine droplets are separated. The water droplets, the average diameter of which lies in the range from about 10 to 30.mu.m, arise in a pressure relaxation in a high pressure valve ("schoke valve"), with it being possible for the pressure drop to amount to a multiple of 100 bar. The values of the droplet diameters scatter strongly about the mean value.
The gas and oil/water mixture flow--in the upper part of the apparatus, or in its lower part respectively--from an intake region to an outlet region. Water and oil separate in this situation thanks to a difference in density; at the outlet region they form a layer of oil which contains only 0.5 to 1% water and a layer of water lying below it which is contaminated by oil. The water must then be treated (e.g. with centrifugal separators) in order to obtain a quality which is tolerable by the environment.
In the inlet region of the three-phase separation apparatus a packing can be installed for the following purposes: If the site of the apparatus during use is, for example, a ship or a floating platform ("offshore sites") then a re-mixing of the three phases as a result of the rolling movement should be prevented; in addition the coalescence of the water droplets should be encouraged. Whereas the first of these goals is attained without doubt, the second appears questionable since most of the droplets do not enter into contact with the surface when flowing through the packing, and thus a coalescence-encouraging effect can be only weakly developed.
This three-phase separation apparatus has a very large volume, which is particularly disadvantageous for offshore sites. Dwell times of from 3 to 10 minutes are required for the oil. The speeds of the phases flowing through the apparatus are on the order of magnitude of several millimeters per second.
Water/oil filters are known in which a coalescence is based on a filtering effect and not on a flow or gravitational effect. These filters can be used only for low water proportions in the range of 1% to 10 ppm water since at higher water proportions the filters become saturated with water and thus become ineffective.
In addition to a separation of water from oil, a separation of oil from water, as is required for example in sea water pollutions after tanker accidents, should also be possible with the separation apparatus.